1. Field of the Invention
The present invention relates to a fuel injection system for a spark-ignition internal combustion engine which is operative to mechanically meter a liquid fuel and intermittently deliver the metered fuel to the engine.
2. Description of the Prior Art
Systems of various types and structures have been proposed for injecting a fuel such as gasoline into internal combustion engines. The heretofore-known types of fuel injection systems include an intermittent injection type in which a fuel is metered by a Jerk type fuel injection pump having a controller comprising a three dimensional cam operative in response to variations in the engine operation speed and in the degree of throttle valve opening to control the metering of the fuel and the metered fuel is delivered by injectors into branches of engine intake manifold.
The Jerk type fuel injection pump is advantageous in that the pump is operative to inject fuel at a high pressure with a resultant improvement in the atomization of the injected fuel. With this type of fuel injection pump, however, the control of the amounts of fuel to be injected into an associated engine depends not upon direct detection of the rate of air flow into the engine but indirectly upon the detection of the engine speed and the throttle valve position. The injection system of the type concerned has a difficulty that the accuracy of the air-fuel ratio control is lowered during use due partly to the wear of components which form mechanical connections and due partly to wear in the engine. In case where a Jerk type injection pump is used with a multicylinder engine, the pump is required to have the same number of elements as that of the engine cylinders and, in addition, necessitates many components which must be worked with a high degree of preciseness, with a resultant increase of the cost of manufacture of the pump. Moreover, the Jerk type injection pump is large-sized and heavy-weighted and thus is difficult to install in an automobile.
U.S. Pat. No. 3,996,910 issued Dec. 14, 1976 to Masaaki Noguchi et al. (inventors of the present application) discloses a fuel injection system comprising a fuel metering and distributing device which includes a rotor and a control shaft. Fuel metering and distributing slits or orifices are formed in the control shaft and in the rotor. The orifice in the rotor is brought into overlapping relationship with successive orifices in the control shaft by the rotation of the rotor to meter and distribute the fuel to respective fuel injectors. The area over which the orifice in the rotor is overlapped with each of the orifices in the control shaft is varied in accordance with a variation in an engine operating parameter, such as the rate of engine intake air flow, to control the rate of fuel flow through the overlapped fuel metering and distributing orifices. The angle of rotation of the rotor relative to the control shaft over which angle the orifice in the rotor is communicated with each of the orifices in the control shaft is constant regardless of the rate of engine intake air flow. The fuel injection system of the described structure and arrangement is difficult to manufacture and to satisfy the requirement for the fuel metering accuracy.